1. Field of the Invention
The present invention relates to a motion control device for a vehicle for controlling a motion of a vehicle by controlling braking force exerted on each wheel of front wheels and rear wheels of the vehicle.
2. Description of the Prior Arts
There has conventionally been a demand for controlling a motion of a vehicle so as to prevent the turning state of the vehicle from being unstable due to the occurrence of an excessive roll angle on the vehicle upon the turning of the vehicle. This roll angle depends upon the magnitude of an actual lateral acceleration that is a component of an acceleration actually exerted on the vehicle in the side-to-side direction of the vehicle body, and increases with the increase of the actual lateral acceleration. On the other hand, the magnitude of the actual lateral acceleration exerted on the vehicle is decreased by producing a yawing moment in the direction opposite to the turning direction of the vehicle or by decelerating the vehicle.
From the above, a motion control device for a vehicle disclosed in Japanese Unexamined Patent Application No. HEI10-119743, for example, controls braking force exerted on each wheel for producing a yawing moment in the direction opposite to the turning direction of the vehicle according to a roll angle of the vehicle body, when the vehicle is turning. According to this, the brake force exerted on each wheel can be controlled such that the yawing moment in the direction opposite to the turning direction of the vehicle is increased according to the increase of the roll angle of the vehicle body, when the vehicle is turning, whereby the magnitude of the lateral acceleration exerted on the vehicle is decreased when the roll angle of the vehicle body is increased. As a result, the occurrence of an excessive roll angle on the vehicle body can be prevented.
However, when the braking force of each wheel is controlled by the above-mentioned device, a yawing moment is caused on the vehicle in the direction opposite to the turning direction of the vehicle, so that the turning state of the vehicle is controlled to be always brought into (or to be close to) an understeer state. Consequently, even when the actual lateral acceleration exerted on the vehicle is small and there is low possibility of the occurrence of the excessive roll angle on the vehicle body, the turning radius of the vehicle becomes greater than the expected turning radius, thereby entailing a problem that there may be a case where a tracing performance cannot satisfactorily be maintained.